<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
    div 
    {
        border: solid 5ps red;
        margin-top: 20px;
        margin-bottom: 20px;
    }
    </style>
</head>
<body>
    <div class="first">蛤蛤</div>
    <div>呵呵</div>
</body>
</html>